/Engine/Source/Runtime/Slate/Public/Framework/Docking/TabManager.h
Check these all tabs to see if it is OK to close them. Ignore the TabsToIgnore
virtual bool CanCloseManager ( const [TSet](API\Runtime\Core\Containers\TSet)< [TSharedRef](API\Runtime\Core\Templates\TSharedRef)< [SDockTab](API\Runtime\Slate\Widgets\Docking\SDockTab) > > & TabsToIgnore )